Honda Power Unit Hardware & Software

[godlameroso]

I don't think anyone would burn fuel when engine braking. Why waste fuel when your air pump (ice) can feed your turbo with air only. Burning fuel on engine braking to harvest though the turbo would be very inefficient.

If your combustion process is more efficient than before it makes it easier to live with such inefficiencies if it means you have more electrical energy. It could be that efficiency improvements let you be inefficient and use the MGU-K to H to ES path to give you a 2% increase of full power mode per lap, while maintaining the same overall fuel efficiency as before the upgrade.

[dren]

The team/s with most efficient power unit will be able to also use party mode>>qualifying mode>>freeload mode sparingly in race when needed because they will be able to compensate for fuel burned by their super efficiency when they get a clear road ahead of them during a race.

Or likewise, they can run the race with less fuel overall for a lap gain and less tire wear.

[saviour stivala]

The team/s with most efficient power unit will be able to also use party mode>>qualifying mode>>freeload mode sparingly in race when needed because they will be able to compensate for fuel burned by their super efficiency when they get a clear road ahead of them during a race.

Or likewise, they can run the race with less fuel overall for a lap gain and less tire wear.

agree.

[henry]

I don't think anyone would burn fuel when engine braking. Why waste fuel when your air pump (ice) can feed your turbo with air only. Burning fuel on engine braking to harvest though the turbo would be very inefficient.

There are two very different use cases. Qualifying and race.

In qualifying any time they can burn fuel to reduce lap time they will.

In the race they only burn sufficient fuel to achieve a race winning time. They calculate this amount before the race and continuously during it.

True. But when they have sufficient energy in the battery in quali, i guess the waste gate will jut be put full open to reduce pumping losses.

That’s not what you were arguing in the post I replied to.

In qualifying during a heavy braking episode it would potentially be useful to burn fuel and drive the MGU-K with the ICE once the load on the rear axle is insufficient to support the traction necessary to drive the K at its max output, 120kW.

Earlier in the braking, at high speed, the K is well short of the power needed at the rear axle so the aim would be to use engine braking to take load off the brakes which are doing the majority of work at this stage. I think the only period when the wastegate might open is just before the K is responsible for all the rear wheel braking.

[saviour stivala]

The waste-gates are open when the ICE is at maximum fueling and the turbo is in electric supercharging mode, at that point both ‘H’ and ‘K’ are sharing ES power, both motoring/deploying. The K harvests only when the brakes are applied.

[henry]

I really wonder how this balance between ice efficiency and mgu-h works. Basically they went from about 30% efficient to 50% in a few years. I think about 1/2 of the exhaust losses are now harvested by mgu-h. It does mean a lot that they sometimes choose to sent more energy into the turbine rather then to increase ice efficiency itself, because the turbine's efficiency itself is only about 50%

Starting with the total heat energy available in the exhaust, the turbine extracts about 27%. This sounds bad but the maximum possible (isentropic efficiency) for a turbine at these temperatures (assume 1000*K exhaust and 300*K ambient) is only 38%. The Carnot efficiency (the "impossible" but theoretical limit) for a heat engine operating between these temperatures is 70%.

and also mhu-h and mgu-k are about 97%, so more losses.
They must be at the very limit with combustion efficiency already.

In terms of converting heat from combustion of fuel into work on the top of the piston (IMEP), they are probably over 50% out of a possible 80%. Not quite at the limit.

I’m struggling to understand the 27% number.

My understanding is that the compressor takes around 100kW to drive and Honda claim they are extracting 70kW with the MGU-H, which puts the turbine at 170kW. 27% efficiency would put the total exhaust energy at 630kW which is about 50% of the energy rate from the fuel. Doesn’t leave much for the cooling system to do.

Where am I going wrong?

[gruntguru]

I really wonder how this balance between ice efficiency and mgu-h works. Basically they went from about 30% efficient to 50% in a few years. I think about 1/2 of the exhaust losses are now harvested by mgu-h. It does mean a lot that they sometimes choose to sent more energy into the turbine rather then to increase ice efficiency itself, because the turbine's efficiency itself is only about 50%

Starting with the total heat energy available in the exhaust, the turbine extracts about 27%. This sounds bad but the maximum possible (isentropic efficiency) for a turbine at these temperatures (assume 1000*K exhaust and 300*K ambient) is only 38%. The Carnot efficiency (the "impossible" but theoretical limit) for a heat engine operating between these temperatures is 70%.

and also mhu-h and mgu-k are about 97%, so more losses.
They must be at the very limit with combustion efficiency already.

In terms of converting heat from combustion of fuel into work on the top of the piston (IMEP), they are probably over 50% out of a possible 80%. Not quite at the limit.

I’m struggling to understand the 27% number.
My understanding is that the compressor takes around 100kW to drive and Honda claim they are extracting 70kW with the MGU-H, which puts the turbine at 170kW. 27% efficiency would put the total exhaust energy at 630kW which is about 50% of the energy rate from the fuel. Doesn’t leave much for the cooling system to do.

Where am I going wrong?

I wasn't aware of those numbers. I assumed the following.
Exhaust temp 1000K
Ambient temp 300K
Exhaust pressure 3 bar (abs)
Turbine efficiency 70%
Exhaust mass flow 0.6 kg/s

Those numbers give a turbine power of 113 kW and heat content of the exhaust at 420 kW.

Working backwards to get turbine power at 170 kW one possibility is 5 bar exhaust pressure and 75% turbine efficiency for a turbine power of 167 kW which is closer to 40% of exhaust energy.

The remaining 60% is very inaccessible. The turbine outlet temperature is 741K (468*C) and the gas is relatively wet so it is not feasible even to extract all the heat, let alone convert it to useful mechanical work. (This relates to "lower" vs "higher" heating values of fuel (LHV vs HHV) where much of the exhaust heat is "latent" heat and impossible to extract. For gasoline, only LHV is typically quoted. HHV is about 7% higher.)

[godlameroso]

Regarding vibrations, it's been shown that frequencies and harmonics can and do affect combustion stability. Perhaps the solution is not in trying to remove it, but rather inducing it so that it happens in a place that won't bother you(within the rev range).

Although common sense dictates that firing order is pretty much set, I wonder how much that is something that has been tinkered with, or if worth doing at all? These aren't conventional engines and aren't subject to the laws of conventional thinking.

[Tommy Cookers]

..... The K harvests only when the brakes are applied.

that's wrong
wrong each and every time you say it

but I won't downvote as you seem to get downvotes mysteriously cancelled

[Tommy Cookers]

...... 27% efficiency would put the total exhaust energy at 630kW which is about 50% of the energy rate from the fuel. Doesn’t leave much for the cooling system to do.

isn't that the point of heat dilution ?
(greatly reducing the heat to be dumped by the cooling system - so increasing the heat working on the piston)

the heat dumped in the exhaust gas (the mass increased with dilution) will not be so much reduced
(question - is there any reduction in heat dumped in the exhaust gas ?)

[henry]

...... 27% efficiency would put the total exhaust energy at 630kW which is about 50% of the energy rate from the fuel. Doesn’t leave much for the cooling system to do.

isn't that the point of heat dilution ?
(greatly reducing the heat to be dumped by the cooling system - so increasing the heat working on the piston)

the heat dumped in the exhaust gas (the mass increased with dilution) will not be so much reduced
(question - is there any reduction in heat dumped in the exhaust gas ?)

I agree, an objective is to reduce the heat going to the cooling system. That is obviously wasted energy, both directly and indirectly, via drag. But assuming the ICE is 45% efficient, ie crank work, that leaves just 5% going to the cooling system, with additional cooling for the ERS and transmission that probably puts the total cooling requirement at 100kW or so, less than half of what it I would guess it was in the normally aspirated era. Maybe that’s how it is.

I take it your question on heat dumped to the exhaust is comparing these engines with engines running at lower AFR?

I doubt there is a simple answer to that. We do know that Honda said that as they improved combustion, crank work went up and the H output went down, or didn’t improve as much. Whether that was because of reduced turbine output or increased compressor demand I don’t know. Similarly I don’t know whether the reduction in mean temperature of the exhaust would reduce the ability of the turbine to extract work.

[godlameroso]

Max theoretical energy in exhaust gases is ~400KW. 25% of that is 100KW, which is more or less max MGU-H output.

[henry]

Max theoretical energy in exhaust gases is ~400KW. 25% of that is 100KW, which is more or less max MGU-H output.

The exhaust gases also drive the compressor.

Where do you get 100kW from?

[godlameroso]

Max theoretical energy in exhaust gases is ~400KW. 25% of that is 100KW, which is more or less max MGU-H output.

The exhaust gases also drive the compressor.

Where do you get 100kW from?

Numbers thrown around here. Numbers needed to produce ~4bar boost pressure. Yes 400kw in exhaust gases the turbine efficiency ~27% theoretical maximum means ~100kw available power for turbine. That 400kw can change with fuel chemistry so lets say 430kw, 24% turbine efficiency, then electronic losses between turbine/mgu-h, in the end its still around 70kw left over. So it stands to reason improving turbine efficiency and ERS interaction will unlock more power.

Compressor efficiency can also unlock more power.

[ringo]

I really wonder how this balance between ice efficiency and mgu-h works.

Basically they went from about 30% efficient to 50% in a few years. I think about 1/2 of the exhaust losses are now harvested by mgu-h.

It does mean a lot that they sometimes choose to sent more energy into the turbine rather then to increase ice efficiency itself, because the turbine's efficiency itself is only about 50% and also mhu-h and mgu-k are about 97%, so more losses.

They must be at the very limit with combustion efficiency already.

The turbine efficiency itself is much higher than that.About 85% at the rated speed. It's the actual speed is the issue with efficiency at any given time (once its not at rated speed)
Also from my calculations, there will be about 220kW available for MGUH, but from what we see the systems aren't extracting all of this power. This may be due to the quality of the heat energy as the egt drops.
For example without MGUH egt is about 970 degrees C. If all the available energy was transfered to MGUH the egt would be about 551C, but none of the teams are able to extract all.
As for Honda it's a question of how efficient the ERS are and the ICE combustion. They may well have the best turbine on the grid and still not able to extract as much power.